Pressure control apparatus

ABSTRACT

Methods and apparatuses are disclosed for applying negative pressure to a wound site. In some embodiments, the apparatus comprises a source of negative pressure, a processing element, and a memory comprising instructions configured to, when executed on the processing element, cause the apparatus to attempt to generate, via the source of negative pressure, a desired negative pressure at the wound site. If the desired negative pressure has not been generated after a first predetermined period of time, the instructions cause the apparatus to: deactivate the source of negative pressure for a second predetermined period of time, and subsequently attempt to generate the desired negative pressure at the wound site.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for applying anegative pressure. In particular, but not exclusively, the presentinvention relates to the application of a negative pressure to a woundsite in the application of topical negative pressure at the wound site.

BACKGROUND OF THE INVENTION

There is much prior art available relating to the provision of apparatusand methods of use thereof for the application of topical negativepressure (TNP) therapy to wounds together with other therapeuticprocesses intended to enhance the effects of the TNP therapy. Examplesof such prior art include those listed and briefly described below.

TNP therapy (sometimes referred to as Vacuum Assisted Closure ornegative pressure wound therapy) assists in the closure and healing ofwounds by reducing tissue oedema; encouraging blood flow and granulationof tissue; removing excess exudates and may reduce bacterial load andthus, infection to the wound. Furthermore, TNP therapy permits lessoutside disturbance of the wound and promotes more rapid healing.

In International patent application, WO 2004/037334, which isincorporated herein by reference, apparatus, a wound dressing and amethod for aspirating, irrigating and cleansing wounds are described. Invery general terms, the application describes the treatment of a woundby the application of TNP therapy for aspirating the wound together withthe further provision of additional fluid for irrigating and/orcleansing the wound, which fluid, comprising both wound exudates andirrigation fluid, is then drawn off by the aspiration means andcirculated through means for separating the beneficial materials thereinfrom deleterious materials. The materials which are beneficial to woundhealing are recirculated through the wound dressing and those materialsdeleterious to wound healing are discarded to a waste collection bag orvessel.

In International patent application, WO 2005/04670, which isincorporated herein by reference, apparatus, a wound dressing and amethod for cleansing a wound using aspiration, irrigation and cleansingare described. Again, in very general terms, the invention described inthis document utilises similar apparatus to that in WO 2004/037334 withregard to the aspiration, irrigation and cleansing of the wound,however, it further includes the important additional step of providingheating means to control the temperature of that beneficial materialbeing returned to the wound site/dressing ‘so that it is at an optimumtemperature, for example, to have the most efficacious therapeuticeffect on the wound.

However, the above described apparatus and methods are generally onlyapplicable to a patient when hospitalised as the apparatus used iscomplex, needing people having specialist knowledge in how to operateand maintain the apparatus, and also relatively heavy and bulky, notbeing adapted for easy mobility outside of a hospital environment by apatient, for example.

Some patients having relatively less severe wounds which do not requirecontinuous hospitalisation, for example, but whom nevertheless wouldbenefit from the prolonged application of TNP therapy, could be treatedat home or at work subject to the availability of an easily portable andmaintainable TNP therapy apparatus. To this end GB-A-2 307 180 describesa portable TNP therapy unit which may be carried by a patient andclipped to belt or harness. A negative pressure can thus be applied at awound site.

However, this portable apparatus is still relatively bulky, and mayrequire monitoring of the patient by a trained caregiver. Furthermore,such portable therapy units commonly have reduced capacity to deal withfluid flow rates into a wound cavity caused by leaks. This leads to agreater number of alarms being raised due to an inability to maintainthe desired negative pressure at the wound site in the presence ofleaks.

Another problem associated with portable apparatus is that on occasionan onboard power source such as a battery pack is used rather than acontinuous connection to a power source such as a mains power source. Itwill be appreciated that such a battery pack has only a limited powerresource and therefore TNP therapy can on occasion be halted prior to adesired moment in time because of power failure.

Another problem associated with therapy units which can be utilised by apatient alone without the need for skilled technical assistants is thatfrom time to time warning lights or warning alarms may be initiated whena desired therapy can not be maintained or initiated. This can bedistressing for a patient who may not understand the meaning of thecues.

A still further problem associated with the apparatus used to provideTNP therapy is that from time to time a motor associated with a pumpwhich generates a negative pressure will start up or stop. The change involume coming from the therapy unit can be a cause of concern to apatient.

SUMMARY OF THE INVENTION

It is an aim of certain embodiments of the present invention to at leastpartly mitigate one or more of the above-mentioned problems.

It is an aim of certain embodiments of the present invention to providea method for controlling the provision of a desired negative pressure ata wound site to aid in wound closure and healing.

It is an aim of certain embodiments of the present invention to providea pressure control apparatus that avoids the generation of unnecessaryalarms in the presence of transient leaks.

It is an aim of certain embodiments of the present invention to providea pressure control apparatus that helps extend battery power lifetime.

It is an aim of certain embodiments of the present invention to providea pressure control apparatus that reduces a number of pump motorstart-up or power down operations.

According to a first aspect of the present invention there is providedapparatus for dressing a wound for the application of topical negativepressure at a wound site, comprising:

-   -   a source of negative pressure;    -   a processing element;    -   a memory comprising instructions configured to, when executed on        the processor, cause the apparatus to perform the steps of:    -   via the source of negative pressure, attempting to generate a        desired negative pressure at the wound site;    -   if the desired negative pressure has not been generated after a        first predetermined period of time, deactivating the source of        negative pressure for a second predetermined period of time; and    -   subsequently attempting to generate the desired negative        pressure at the wound site.

According to a second aspect of the present invention there is provideda method of applying topical negative pressure (TNP) at a wound site,comprising the steps of:

-   -   via a source of negative pressure, attempting to generate a        desired negative pressure at the wound site;    -   if the desired negative pressure has not been generated after a        first predetermined period of time, deactivating the source of        negative pressure for a second predetermined period of time; and    -   subsequently attempting to generate the desired negative        pressure at the wound site.

According to a third aspect of the present invention there is providedan apparatus for applying negative pressure to a wound, comprising:

-   -   a source of negative pressure coupled to a dressing; and    -   a controller configured to:        -   activate the source of negative pressure to generate a first            desired negative pressure under the dressing;        -   if, upon an expiration of a first time interval, a negative            pressure under the dressing has not reached the first            desired negative pressure, deactivate the source of negative            pressure for a second time interval; and        -   upon expiration of the second time interval, activate the            source of negative pressure to generate the first desired            negative pressure under the dressing.

In some embodiments, the controller is further configured to: deactivatethe source of negative pressure when the first desired negative pressurehas not been generated under the dressing after activating the source ofnegative pressure for a first number of times exceeding a firstthreshold.

In some embodiments, the controller is further configured to: when thefirst number of times exceeds the first threshold, deactivate the sourceof negative pressure for a third time interval.

In some embodiments, the apparatus further comprises: a switchconfigured to signal to the controller to activate or deactivate thesource of negative pressure; and the controller is further configuredto, upon expiration of the third time interval or upon receiving asignal to activate the source of negative pressure from the switch,activate the source of negative pressure to generate the first desirednegative pressure under the dressing.

In some embodiments, the apparatus further comprises: an indicator,wherein the controller is further configured to activate the indicatorwhen the first number of times exceeds the first threshold.

In some embodiments, the controller is further configured to: deactivatethe indicator upon expiration of the third time interval or receiving asignal to activate the source of negative pressure from the switch.

In some embodiments, the indicator indicates a leak in the seal.

In some embodiments, the controller is further configured to:

-   -   when the negative pressure under the dressing has reached the        first desired negative pressure, deactivate the source of        negative pressure and monitor negative pressure under the        dressing; and    -   if the negative pressure under the dressing drops below a        negative pressure threshold, activate the source of negative        pressure to generate a second desired negative pressure under        the dressing.

In some embodiments, the first and second desired negative pressure arethe same.

In some embodiments, the second desired negative pressure is less thanthe first desired negative pressure.

In some embodiments, the controller is further configured: to deactivatethe source of negative pressure if the negative pressure under thedressing has reached the second desired negative pressure or if thenegative pressure under the dressing has not reached the second desirednegative pressure upon expiration of a fourth time interval.

In some embodiments, if the negative pressure under the dressing has notreached the second desired negative pressure upon expiration of thefourth time interval, the controller is further configured to, uponexpiration of the second time interval, activate the source of thenegative pressure to generate the first desired negative pressure underthe dressing.

In some embodiments, the controller is further configured to: activatethe source of the negative pressure to generate the first desirednegative pressure under the dressing if the controller has activated thesource of negative pressure to reach the second desired negativepressure for a second number of times less than a second threshold.

In some embodiments, the controller is further configured to:

-   -   deactivate the source of negative pressure if the controller has        activated the source of negative pressure to reach the second        desired negative pressure for the second number of times        exceeding the second threshold; and    -   upon expiration of the third time interval or upon receiving the        signal from the switch to activate the source of negative        pressure, activate the source of negative pressure to generate        the first desired negative pressure under the dressing.

In some embodiments, the controller is further configured to:

-   -   monitor a duty cycle of the source of negative pressure; and    -   deactivate the source of negative pressure if the duty cycle        exceeds a first duty cycle threshold without the negative        pressure reaching the first or second desired negative pressure        under the dressing.

In some embodiments, the duty cycle comprises an amount, proportion, orpercentage of time the source of negative pressure is active over aperiod of time.

In some embodiments, the controller is further configured to: calculatea number of duty cycles that exceed the first duty cycle threshold anddeactivate the source of negative pressure when the number of dutycycles that exceed the first duty cycle threshold exceeds a second dutycycle threshold.

In some embodiments, the controller is further configured to calculate anumber of consecutive duty cycles that exceed the first duty cyclethreshold.

In some embodiments, the second duty cycle threshold comprises 30minutes.

In some embodiments, the controller is further configured: to uponexpiration of the third time interval or upon receiving the signal fromthe switch to active the source of negative pressure, activate thesource of negative pressure to generate the first desired negativepressure under the dressing.

In some embodiments, the source of negative pressure comprises a pump.

In some embodiments, the apparatus further comprises: a pressure sensorconfigured to sense pressure under the dressing and to communicate thesensed pressure to the controller.

In some embodiments, the apparatus further comprises: a one-way valvecoupled between an inlet and the source of negative pressure, whereinthe inlet is in fluid communication with the dressing.

In some embodiments, the source of negative pressure comprises: a valveconfigured to connect the port to an external source of negativepressure.

In some embodiments, the controller is further configured to: activateor deactivate the source of negative pressure by operating the valve.

According to a fourth aspect of the present invention there is provideda method of applying negative pressure to a wound, comprising:

-   -   positioning a dressing over the wound to create a substantially        fluid impermeable seal over the wound;    -   coupling a source of negative pressure to the dressing;    -   activating the source of negative pressure to generate a first        desired negative pressure under the dressing;    -   if, upon an expiration of a first time interval, a negative        pressure under the dressing has not reached the first desired        negative pressure, deactivating the source of negative pressure        for a second time interval; and    -   upon expiration of the second time interval, activating the        source of negative pressure to generate the first desired        negative pressure under the dressing.

In some embodiments, the method further comprises: deactivating thesource of negative pressure when the first desired negative pressure hasnot been generated under the dressing after activating the source ofnegative pressure for a first number of times exceeding a firstthreshold.

In some embodiments, the method further comprises: deactivating thesource of negative pressure for a third time interval when the firstnumber of times exceeds the first threshold.

In some embodiments, the method further comprises: activating the sourceof negative pressure to generate the first desired negative pressureunder the dressing upon expiration of the third time interval or uponreceiving a signal to activate the source of negative pressure from aswitch.

In some embodiments, the method further comprises: indicating to a userwhen the first number of times exceeds the first threshold.

In some embodiments, the method further comprises: stopping theindication upon expiration of the third time interval or receiving asignal to activate the source of negative pressure from the switch.

In some embodiments, the indicating indicates a leak in the seal.

In some embodiments, the method further comprises:

-   -   when the negative pressure under the dressing has reached the        first desired negative pressure, deactivating the source of        negative pressure and monitoring negative pressure under the        dressing; and    -   if the negative pressure under the dressing drops below a        negative pressure threshold, activating the source of negative        pressure to generate a second desired negative pressure under        the dressing.

In some embodiments, the first and second desired negative pressure arethe same.

In some embodiments, the second desired negative pressure is less thanthe first desired negative pressure.

In some embodiments, the method further comprises: deactivating thesource of negative pressure if the negative pressure under the dressinghas reached the second desired negative pressure or if the negativepressure under the dressing has not reached the second desired negativepressure upon expiration of a fourth time interval.

In some embodiments, the method further comprises: if the negativepressure under the dressing has not reached the second desired negativepressure upon expiration of the fourth time interval, activating thesource of the negative pressure to generate the first desired negativepressure under the dressing upon expiration of the second time interval.

In some embodiments, the method further comprises: activating the sourceof the negative pressure to generate the first desired negative pressureunder the dressing if the source of negative pressure has been activatedto reach the second desired negative pressure for a second number oftimes less than a second threshold.

In some embodiments, the method further comprises:

-   -   deactivating the source of negative pressure if the source of        negative pressure has been activated to reach the second desired        negative pressure for the second number of times exceeding the        second threshold; and    -   upon expiration of the third time interval or upon receiving the        signal from the switch to activate the source of negative        pressure, activating the source of negative pressure to generate        the first desired negative pressure under the dressing.

In some embodiments, the method further comprises:

-   -   monitoring a duty cycle of the source of negative pressure; and    -   deactivating the source of negative pressure if the duty cycle        exceeds a first duty cycle threshold without the negative        pressure reaching the first or second desired negative pressure        under the dressing.

In some embodiments, the duty cycle comprises an amount, proportion, orpercentage of time the source of negative pressure is active over aperiod of time.

In some embodiments, the method further comprises: calculating a numberof duty cycles that exceed the first duty cycle threshold anddeactivating the source of negative pressure when the number of dutycycles that exceed the first duty cycle threshold exceeds a second dutycycle threshold.

In some embodiments, the method further comprises: calculating a numberof consecutive duty cycles that exceed the first duty cycle threshold.

In some embodiments, the second duty cycle threshold comprises 30minutes.

In some embodiments, the method further comprises: upon expiration ofthe third time interval or upon receiving the signal from the switch toactive the source of negative pressure, activating the source ofnegative pressure to generate the first desired negative pressure underthe dressing.

In some embodiments, the source of negative pressure comprises a pump.

In some embodiments, the method further comprises sensing pressure underthe dressing.

In some embodiments, the method further comprises: activating ordeactivating the source of negative pressure by operating a valve.

Certain embodiments of the present invention provide the advantage thatthe raising of alarms due to transient leaks into a wound chamber can beavoided, while also reducing the potential for drawing contaminants intoa wound site through a leak into the wound chamber.

Certain embodiments of the present invention provide the advantage ofextending the useful life of a battery powered source of negativepressure used to provide a desired negative pressure to a wound site.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described hereinafter,by way of example only, with reference to the accompanying drawings inwhich:

FIG. 1 illustrates an arrangement for applying negative pressure woundtherapy to a wound site;

FIG. 2 illustrates a schematic representation of a pressure controlapparatus;

FIG. 3 illustrates a schematic representation of a further pressurecontrol apparatus;

FIG. 4 illustrates a state diagram of a controller; and

FIG. 5 illustrates a controller.

In the drawings like reference numerals refer to like parts.

DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS

FIG. 1 illustrates an arrangement for applying negative pressure woundtherapy to a wound site 10. A packing material 12 is placed within awound cavity, and then a drape 14 sealed to the surface of the skinaround the wound site 10 forming a fluid tight seal around the perimeterof a wound chamber. A source of negative pressure, such as a pressurecontrol apparatus 100 is coupled to the wound cavity via a tube 16. Afluid collection canister (not shown) may be coupled between thepressure control apparatus 100 and the wound chamber to collect anywound exudate drawn from the wound site 10. The use of the packingmaterial 12 is optional, and it may be omitted in certain arrangementsas appropriate.

Alternatively, a self contained wound dressing may be used in place ofthe drape, such a wound dressing absorbs wound exudate within the layersof the dressing removing the need for a separate fluid collectioncanister.

Further details regarding wound dressings that may be used incombination with the embodiments described herein are found in U.S.application Ser. No. 13/092,042, filed Apr. 21, 2011, the entirety ofwhich is hereby incorporated by reference.

It is envisaged that the negative pressure range for the apparatus incertain embodiments of the present invention may be between about −50mmHg and −200 mmHg (note that these pressures are relative to normalambient atmospheric pressure thus, −200 mmHg would be about 560 mmHg inpractical terms). Aptly, the pressure range may be between about −75mmHg and −150 mmHg. Alternatively a pressure range of upto −75 mmHg,upto −80 mmHg or over −80 mmHg can be used. Also aptly a pressure rangeof below −75 mmHg could be used. Alternatively a pressure range of over−100 mmHg could be used or over −150 mmHg.

FIG. 2 illustrates a schematic representation of a pressure controlapparatus 100 according to embodiments of the invention that can be usedto apply negative pressure to a wound site 10. The pressure controlapparatus includes an inlet 102 coupled to a pressure sensor 116, andalso to an inlet of a pump 106 via a one-way check valve 104. The pumpis operated by an electric motor 108, which draws power from a battery114. A controller 112 is coupled to the pressure sensor 116 and providescontrol signals for controlling the operation of the electric motor 108.Indicators 110 are coupled to the controller 112 to allow audio and/orvisual feedback of status signals to a user. An outlet of the pump 106is coupled to an outlet 118 of the pressure control apparatus. A usercan utilise a power button 120 to initiate or terminate operation.

The pump 106 shown is a diaphragm pump which may be highly efficient andcapable of providing the required negative pressure. It will beappreciated that other types of pump such as peristaltic pumps, or thelike can be used. In some arrangements, the one-way check valve 104 mayform part of the pump 106, and may not exist as a separate element ofthe apparatus.

While the apparatus has been described as being battery powered, it willbe understood that the apparatus could alternatively draw electricalpower from a mains power supply and the battery power cell removed. Insome arrangements, the apparatus may be capable of being powered fromeither a mains power supply or a rechargeable battery that may berecharged from the mains power supply.

In operation, the inlet 102 is coupled to a wound chamber formed over awound site 10, for example via the length of tube 16. The electric motor108 drives the pump 106 under the control of the controller 112 toprovide a negative pressure at the inlet 102. The negative pressure canthen be communicated to the wound chamber in order to provide a desirednegative pressure at the wound site. The check valve 104 maintains thelevel of negative pressure at the inlet 102 when the pump 106 is notactive and helps avoid leaks.

Upon initially connecting the pressure control apparatus 100 to thewound chamber, the pressure at the wound site will be equal toatmospheric pressure, and an initial pump-down must be performed toestablish the desired negative pressure at the wound site. This mayrequire the pump 106 to be operated for an extended period of time untilthe desired negative pressure is achieved.

The pressure at the inlet 102 is indicative of the pressure experiencedat the wound site, and this pressure is measured by the pressure sensor116. The controller 112 receives the pressure value measured at thepressure sensor 116, and once the measured pressure reaches the desirednegative pressure, the controller deactivates the pump 106. Thecontroller 112 then continues to monitor the pressure at the pressuresensor.

If during the initial pump-down phase, the controller 112 determinesthat the desired negative pressure has not been achieved within acertain time (for example 10 minutes or 20 minutes or 30 minutes or 40minutes or the like), then leaks may be present into the wound chamber,and this condition is signalled via the indicators 110 to show that thewound chamber has not been correctly sealed, or some other error orfault is present.

Once the desired negative pressure has been established, the controller112 monitors the pressure at the inlet of the pressure controlapparatus. From time to time, leaks of fluid may occur into the woundchamber, reducing the level of negative pressure experienced at thewound site, or in other words increasing the absolute pressure at thewound site. The pressure value measured at the pressure sensor 116 andprovided to the controller 112 will therefore increase as fluid leaksinto the wound chamber. When the measured negative pressure value dropsbelow a certain defined pressure level, the controller 112 willreactivate the pump 106 in order to re-establish the desired negativepressure at the wound site. The desired negative pressure and thedefined pressure level at which the controller reactivates the pumpprovide hysteresis limits between which the pressure should bemaintained to apply topical negative pressure to the wound site.

However, if a leak forms that allows fluid, for example air, to leakinto the wound chamber with a flow rate greater than the maximum pumpcapacity 106, it will not be possible for the pressure control apparatus100 to maintain the desired negative pressure at the wound site. If thepressure control apparatus 100 continued to attempt to re-establish thedesired negative pressure in the presence of such a leak, the batterypower cell 114 would become depleted.

Furthermore, continued operation of the pump in the presence of a largeleak can draw contaminants into the wound site, and lead to excessivedrying of the wound site which is undesirable. Therefore, the controller112 is configured to deactivate the pump 106 if the desired negativepressure is not re-established after operation of the pump 106 for apredetermined period of time. For example sometime between around 30minutes and 4 hours.

The formation of leaks into the wound chamber may occur due to a rangeof factors. One common cause of such leaks is movement of a patientbeing treated with the pressure control apparatus 100. For example, aleak may form when a patient moves from a lying to a sitting position,or during the normal range of movement when walking. Such leaks may betransient, and have been found to regularly reseal as the patientcontinues to move or returns to their previous position. Thus, there isa risk that the pump 106 may be deactivated due to the detection of aleak that subsequently reseals. However, once the leak reseals,operation of the pressure control apparatus would be able tore-establish the desired negative pressure within the wound chamber.

According to embodiments of the invention, the controller 112 isconfigured to deactivate the pump 106 after the pump has operated for acertain period of time without the desired level of negative pressurebeing reached in the wound chamber. That is a timeout event occurs. Thecontroller then waits for a further period of time before a retryattempt is made to re-establish the desired negative pressure at thewound site using the pump 106. If the leak has resealed while the pumphas been temporarily deactivated, the retry attempt to re-establish thedesired negative pressure will be successful, and operation of thepressure control apparatus 100 can continue as normal. However, if theleak is still present a further timeout event will occur and the pumpwill be deactivated for the further period of time.

This cycle of deactivating the pump 106 and then attempting tore-establish the desired negative pressure may be repeated a number oftimes in order to provide an opportunity for any leaks to reseal.However, once a timeout event occurs the negative pressure at the woundsite will start to degrade, and therefore there will be a break in thenegative pressure wound therapy applied to the wound site. While a shortbreak in therapy may not be a concern, an extended period in which thenegative pressure is not applied should preferably be avoided.Furthermore, if a leak path into the wound chamber exists for anextended period of time, the potential for contaminants reaching thewound site increases. Thus, if a number, N, of unsuccessful attempts aremade to re-establish the desired negative pressure it can be assumedthat the leak is permanent, and not transient, and the controller 112disables operation of the pressure control apparatus 100 and provides asignal via an audio and/or visual cue to a user that attention isrequired. This allows a patient or caregiver to arrange for anydressings or drapes to be changed to thereby reform the wound chamberand allow the negative pressure wound therapy to be continued. Aptly Nis an integer between 1 and 5 inclusive.

Alternatively, the pump 106 and motor 108 may be omitted, and thenegative pressure may be provided via an external source of negativepressure, such as by connection to a vacuum line or vacuum reservoir.FIG. 3 provides a schematic representation of a further pressure controlapparatus 200 for use with an external source of negative pressure, andwhich can be used to provide negative pressure to a wound site 10.Pressure control apparatus 200 includes a controllable valve 202 coupledbetween an inlet 102 and an outlet 118. The outlet 118 is coupled to theexternal source of negative pressure. Controller 212 provides controlsignals to the valve 202 to control the coupling of the external sourceof negative pressure to the inlet 102, and thereby to the wound chamber.The pressure at the inlet 102 is monitored by a pressure sensor 116,coupled to the inlet, and this monitored pressure is supplied to thecontroller 212.

The operation of the pressure control apparatus 200 of FIG. 3 is similarto that of the pressure control apparatus 100, except that pressure iscontrolled by operating the valve 202 to couple the wound chamber to theexternal source of negative pressure. Controller 112 is able to controlthe level of negative pressure at the inlet 102 by controlling the valve202. By monitoring the pressure at the inlet via the pressure sensor116, the controller 212 can control the valve to provide the desirednegative pressure at the wound site.

Unlike the pressure control apparatus of FIG. 2, an extended attempt toprovide the desired negative pressure in the presence of a leak will notlead to depletion of a battery power cell. However, longterm it is stillundesirable to continue to apply a negative pressure in the presence ofa leak due to the possibility of drawing contaminants into the woundchamber, and of drying out the wound site due to the flow of air throughthe chamber. Thus, the controller 212 of FIG. 3 implements the samecontrol flow as described above with respect to the pressure controlapparatus 100. That is, controller 212 is configured to de-couple theinlet 102 from the external source of negative pressure by closing thevalve if the desired negative pressure is not established at the woundsite within a predetermined period of time. A number of attempts maythen be made to re-establish the desired negative pressure in order toprovide the opportunity for transient leaks into the wound chamber toreseal.

Thus, the pressure control apparatus of FIGS. 2 and 3 are able tocontrol the application of negative pressure to a wound site, andadvantageously reduce the number of alarms due to transient leaks offluid into the wound chamber. When a leak forms that allows air into thewound chamber at a flow rate above a certain level, the pressure controlapparatus is configured to disable the provision of negative pressure tothe wound chamber for a predetermined period of time, providing anopportunity for the leak to reseal. Then, if the leak is transient andreseals, the desired negative pressure may then be re-established at asubsequent attempt. This avoids the need to indicate an alarm conditionfor transient leaks, and also avoids the problem of drawing contaminantsand excessive amounts of air into the wound chamber. This also avoids apump motor being repeatedly energised and de-energised which avoidsconcerning noise level changes and helps improve pump motor longevity.

Controller 112, 212 may be implemented as a microcontroller, or anapplication specific integrated circuit, or the like, and may executeinstructions to provide the above described control functions. Forexample, a suitable microcontroller would be one from the STM8L MCUfamily from ST Microelectronics, for example ST MicroelectronicsSTM8L151G4U6, or one from the MC9S08QE4/8 series from Freescale, such asthe Freescale MC9S08QE4CWJ.

The operation of the controller 112 may be described as a finite statemachine. The operation of the controller is described below withreference to FIG. 4 which shows a state diagram 300 describing theoperation of the controller 112 for the pressure control apparatus shownin FIG. 1.

FIG. 5 illustrates one embodiment of controller 112. The controllercomprises a memory 502, which may hold program code for implementing thecontrol functions. The memory is coupled to a microcontroller 504 ableto execute the instructions. The microcontroller is coupled to inputs506 and outputs 508 through which the microcontroller is able to monitorthe operation of the system and provide control signals to other partsof the pressure control apparatus.

Referring again to FIG. 4 upon activation 310 of the pressure controlapparatus 100 which may occur when an activation strip is pulled for thefirst time or a user button is pressed or the like, the controller 112performs a power-on self test (POST) 302 to ensure that the pressurecontrol apparatus is operating correctly. If the power-on self test isfailed the pressure control apparatus should not be used Therefore,after a failed POST, the controller transitions to a non-recoverableerror state 304 and the error is signalled to the user via indicators110. If the POST is passed, the controller 112 transitions to anoperational state 308 via a standby state, and performs an initial pumpdown 312 when a user indicates via a button, in which the pump 106 isoperated until a desired negative pressure is established in the woundchamber. Alternatively, the controller may wait on a user input beforeperforming the initial pump-down in state 312.

Once the desired negative pressure has been successfully established,the controller transitions to the monitor pressure state 316. However,if after a predetermined period of time the desired pressure has notbeen established and the initial pump down state 312 is unable toestablish the desired negative pressure (indicative of a leak), atimeout occurs. On the first timeout, the controller will transition toa wait state 314, in which the controller waits for a period of timebefore transitioning back to the initial pump down state 312. Furthertimeouts may occur from the initial pump-down state 312, and thecontroller maintains a count of the number of retry attempts made. Oncethe desired negative pressure has been established, the number of retryattempts may be reset.

If a timeout occurs and the number of retry cycles is greater than apredefined maximum number of retry attempts allowed, the controllertransitions to a paused state 306. While in the paused state 306 thecontroller will transition from the paused state 306 to the initial pumpdown state 312 in response to a user input, or after a maximum pausetime.

In the monitor pressure state 316, the controller monitors the pressuremeasured at the pressure sensor 116 and, if the pressure drops out ofthe desired pressure range, the controller transitions to a maintenancepump-down state 318. In the maintenance pump-down state 318, the suctionpump is activated either for a predetermined period of time, for examplebetween around 10 and 60 seconds, or until the desired negative pressureis re-established in the wound chamber, whichever occurs sooner.

It is noted that some hysteresis is built into the desired pressurerange, such that the pressure value, a minimum desired negativepressure, that triggers a transition from the monitor pressure state 316to the maintenance pump-down state 318 is lower than the desirednegative pressure established in the wound chamber by operation of thepump during the maintenance pump-down state 318. For example, taking theoperating pressure ranges discussed above, the desired negative pressuremay be −150 mmHg and the minimum desired negative pressure may be −75mmHg. Alternatively, the controller may act to maintain the pressurewithin a certain percentage range of the desired negative pressure, forexample a 5% hysteresis may be used.

If the desired negative pressure is reached before the suction pump hasbeen operating for the predetermined period of time, the controllertransitions back to the monitor pressure state 316.

However, if the pump operates for the predetermined period of timewithout the desired negative pressure being re-established in the woundchamber, normally due to a leak into the wound chamber, the pressurecontrol apparatus will signal the presence of a leak. If the pressure iswithin the hysteresis limits, i.e. between the minimum desired negativepressure and the desired negative pressure, this signifies the presenceof a high leak, having a flow rate similar to the capacity of the pump.In this situation, the pump continues to operate until the desirednegative pressure is re-established, or until the pressure at the woundsite is no longer held within the hysteresis limits.

If in the presence of a large leak, the desired negative pressure isrestored before a maximum maintenance time is reached, the controllerwill transition back to the monitor pressure state 316, but will signalthe presence of a leak. However, if the suction pump is operated formore than the maximum maintenance time to restore the desired negativepressure, the controller will transition to the paused state 306, whilesignalling the presence of a leak.

If during the maintenance pump-down state 318, the pressure in the woundchamber is not maintained within the hysteresis limits, a catastrophicleak has occurred, and the controller transitions to the wait state 314.

In some embodiments, if after a predetermined period of time, thedesired pressure has not been established and the maintenance pump downstate 318 is unable to establish the desired negative pressure beforethe maximum maintenance time is reached, a timeout occurs. On the firsttimeout, the controller will transition to the wait state 314, in whichthe controller waits for a period of time before transitioning back tothe initial pump down state 312. Further timeouts may occur from themaintenance pump-down state 318, and the controller maintains a count ofthe number of retry attempts made. Once the desired negative pressurehas been established in the maintenance pump down state 318, the numberof retry attempts may be reset. If a timeout occurs and the number ofretry attempts is greater than a predefined maximum number of retryattempts allowed, the controller transitions to the paused state 306, asdescribed above.

Thus, if the leak is such that it is over a prescribed limit and thepump duty cycle (DC) as defined, in some embodiments, as pump on timedivided by pump off time is over a predetermined limit then the pumpshall continue to operate within the hysteresis limits for a particulartime duration. For example, around 30 minutes as shown in FIG. 4. Thus,in the monitor pressure loop if the duty cycle is less than apredetermined limit then all is okay. If the duty cycle is greater thana particular limit but less than a time out time the pump continues torun for up to 30 minutes. If DC is greater than time out then a pausedstate 306 is entered.

At any time while in the operational state 308, the controller may beplaced in the pause state 306 in response to a user input. Once thebattery voltage reaches a low voltage cut off level or the lifetime ofthe pressure control apparatus has been reached, the controllerde-activates the pressure control apparatus and an End of Life state isreached.

The controller 212 described with respect of the pressure controlapparatus 200 of FIG. 3 operates in a similar manner as described aboveexcept that the initial pump-down and maintenance pump-down states arereplaced with valve activation states in which the inlet 102 is coupledto the external source of negative pressure connected to the outlet 118via controllable valve element 202.

Alternatively, the POST state 302 may be omitted.

The pressure control apparatus may be configured to be re-useable and beprovided with a switch to allow the apparatus to be turned on and off asrequired. Such a re-usable apparatus may include rechargeable powercells, and may provide a low power indication in order to allow thepower cells to be replaced/recharged.

In a disposable single use pressure control apparatus, activation may beprovided by pulling an activation strip and it may not be possible todeactivate the apparatus once activated until the apparatus is to bediscarded.

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of the words, for example“comprising” and “comprises”, means “including but not limited to”, andis not intended to (and does not) exclude other moieties, additives,components, integers or steps.

Throughout the description and claims of this specification, thesingular encompasses the plural unless the context otherwise requires.In particular, where the indefinite article is used, the specificationis to be understood as contemplating plurality as well as singularity,unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties orgroups described in conjunction with a particular aspect, embodiment orexample of the invention are to be understood to be applicable to anyother aspect, embodiment or example described herein unless incompatibletherewith.

1-38. (canceled)
 39. A method of treating a wound implemented by acontroller of a negative pressure wound therapy device, the methodcomprising: in response to receiving a request from a user interface ofthe negative pressure wound therapy device to initiate negative pressurewound therapy, activating a source of negative pressure to attempt togenerate a desired negative pressure at the wound; if the desirednegative pressure has not been reached after a first period of time,deactivating the source of negative pressure for a second period oftime; and subsequently attempting to generate the desired negativepressure at the wound.
 40. The method as claimed in claim 39, furthercomprising: if the desired negative pressure has not been reached aftera third period of time, deactivating the source of negative pressure forthe second period of time, and subsequently attempting to generate thedesired negative pressure at the wound.
 41. The method as claimed inclaim 40, further comprising: when the desired negative pressure has notbeen reached after the third period of time, deactivating the source ofnegative pressure for the second period of time and subsequentlyattempting to generate the desired negative pressure at the wound. 42.The method as claimed in claim 40, further comprising: deactivating thesource of negative pressure when the desired negative pressure has notbeen reached after a threshold number of attempts.
 43. The method asclaimed in claim 42, further comprising: providing an indication whenthe desired negative pressure has not been reached after the thresholdnumber of attempts.
 44. The method as claimed in claim 39, wherein thesource of negative pressure comprises a pump, and activating the sourceof negative pressure comprises activating the pump.
 45. The method asclaimed in claim 44, wherein deactivating the source of negativepressure comprises deactivating the pump.
 46. The method as claimed inclaim 39, wherein: the source of negative pressure comprises a valveconfigured to be coupled to an external source of negative pressure andactivating the source of negative pressure comprises opening the valve.47. The method as claimed in claim 46, wherein deactivating the sourceof negative pressure comprises closing the valve.
 48. The method asclaimed in claim 39, further comprising: monitoring a duty cycle of thesource of negative pressure; and deactivating the source of negativepressure if the duty cycle satisfies a duty cycle threshold withoutsuccessfully reaching the desired negative pressure at the wound. 49.The method as claimed in claim 48, wherein the duty cycle comprises anamount of time the source of negative pressure is active over a timeperiod.
 50. The method as claimed in claim 39, further comprising:monitoring a plurality of duty cycles of the source of negativepressure; calculate a number of duty cycles from the plurality of dutycycles that satisfy a first duty cycle threshold; and deactivating thesource of negative pressure if the number of duty cycles satisfies asecond duty cycle threshold.
 51. The method as claimed in claim 39,further comprising: monitoring negative pressure at the wound; and ifthe monitored negative pressure is below a threshold negative pressure,attempting to generate the desired negative pressure at the wound. 52.The method as claimed in claim 51, wherein: the threshold negativepressure is more positive than the desired negative pressure.
 53. Themethod as claimed in claim 39, further comprising: maintaining thedesired negative pressure at the wound after the desired negativepressure at the wound has been reached.
 54. The method as claimed inclaim 53 wherein maintaining comprises: monitoring a level of negativepressure at the wound; and when it has been determined that the level ofnegative pressure at the wound is more positive that a pressurethreshold, activating the source of negative pressure to attempt togenerate the desired negative pressure at the wound.
 55. The method asclaimed in claim 54, further comprising: deactivating the source ofnegative pressure when desired negative pressure has been reached. 56.The method as claimed in claim 55, further comprising: deactivating thesource of negative pressure when desired negative pressure has not beenreached after a third period of time.
 57. The method as claimed in claim39, further comprising: providing an indication if the desired negativepressure has not been reached after the first period of time.
 58. Themethod as claimed in claim 39, further comprising: providing anindication when the desired negative pressure at the wound has beenreached.